1. Field of the Invention
The present invention relates to a mobile communication system. More particularly, the present invention relates to a method and apparatus for transmitting/receiving data on multiple carriers in the mobile communication system.
2. Description of the Related Art
Mobile communication systems have developed to provide subscribers with mobile voice communication services. With the advance of technology, mobile communications have evolved to support high speed data communication services as well as the standard voice communication services.
Recently, as a next generation mobile communication system, a standard for Long Term Evolution (LTE) is being discussed by the 3rd Generation Partnership Project (3GPP). LTE is designed to provide a downlink speed of up to 100 Mbps.
More recent studies are focused on the LTE-Advanced (LTE-A) for improving data rate with the adaptation of several new techniques. Carrier Aggregation is one of the most distinct features of LTE-A. Unlike the a communication system using single uplink and single downlink carriers per User Equipment (UE), the carrier aggregation enables a UE to be scheduled on multiple carriers in both uplink and downlink.
By taking notice that a cell is configured with one downlink carrier and one uplink carrier, the carrier aggregation may be understood as if the UE communicates data via multiple cells. With the use of carrier aggregation, the maximum data rate increases in proportion to the number of aggregated carriers.
In the following description, if a UE receives data through a certain downlink carrier or transmits data through a certain uplink carrier, data is transmitted or received through control and data channels provided in a cell corresponding to center frequencies and frequency bands of the downlink and uplink carriers.
In the following description, carrier aggregation may be expressed in such a way that multiple serving cells are configured. The multiple serving cells include a Primary serving cell (PCell) and at least one Secondary serving Cell (SCell).
As used herein, the terms used to describe the embodiments of the present invention have the meanings as they do in LTE and as described in 3GPP TS36.331 and TS36.321.
The legacy technology-based UE performs random access only to the PCell. If the UE attempts random access only to the PCell, this may cause SCell uplink performance degradation of the UE. The UE is likely to fail uplink transmission in the SCells particularly when the PCell and SCells have different uplink transmission timings